1. Field of the Invention
The invention relates to an electric vehicle and a method of controlling the electric vehicle, and particularly relates to an electric vehicle in which an electric motor generates driving force for running the vehicle, using electric power output from an electric storage device, and a method of controlling the electric vehicle.
2. Description of Related Art
A controller of an electric vehicle that obtains energy for running the vehicle from a storage battery is disclosed in Japanese Patent Application Publication No. 8-23603 (JP 8-23603 A). The controller determines that the remaining battery charge of the storage battery has been reduced if the voltage of the storage battery is kept at a low level for a given period of time, and restricts a torque command value to be output to an electric motor by reducing the command value at a given rate of reduction. As a result, the torque of the electric motor is reduced, and the electric power required to be output from the storage battery is reduced, so that the vehicle can keep running without causing the voltage of the storage battery to be rapidly or sharply reduced.
In the controller as described above, the restriction of the torque command is cancelled when the operation amount of the accelerator pedal becomes equal to zero. In this condition, if the accelerator pedal is depressed again, the voltage of the storage battery is naturally reduced. However, since it takes some period of time until this condition is detected, the electric motor can generate torque required to accelerate the vehicle within this period of time. As a result, the vehicle can be accelerated or run at a high load, as needed (see JP 8-23603 A).
In the controller as described in JP 8-230603 A, the restriction of the torque command is cancelled when the operation amount of the accelerator pedal becomes equal to zero. However, a specific method or manner of cancelling restriction of the torque command has not been studied. In this connection, it is deemed desirable to promptly cancel restriction of the output when appropriate; however, if the accelerator pedal is depressed under a situation where the output is likely to be restricted again, after cancellation of the output restriction, the output may be restricted immediately after acceleration, resulting in deterioration of the driveability.